Get a factory fresh SDCard, write plain Raspbian 2018-11-13 to it using Etcher.
Boot that new system. Mount the unreadable SDCard in a USB reader. Mount the USB reader in your RPi and see if you can undo the damage.

:lol: I was just trying to make a point so that people can see that it would be beneficial if it could be implemented for a low price. What possible use does it have? It's like reading the cpu temperature, what can you do if you don't like the numbers? If I know the power budget is limited I apply ...

I would have thought the best experiment would be to load plain Raspbian 2018-11-13 onto a blank USB device and see what happens with that. Then look at the 4.19 kernel (which is being tested with sudo BRANCH=next rpi-update) then look at moving your application on to a supported/supportable version...

You think everything is a bad idea. And don't often back up your arguments. You were spitting feathers about minicom the last time our paths crossed. Finally, I can think of 3 obvious reasons why using cron as you describe is a bad idea. They are so obvious that I won't bother writing them out now....

There is no value in running anti-virus junk. Most of the stuff out there is to protect filesystem shares from Windows virii. If you follow sane and secure security practices (ie don't put a Pi on the public internet with user=pi and password=raspberry) you are unlikely to be a target for the bad ac...

1. Do you recommend to install kernel 4.19 now? Is It stable? 2. Can I back to kernel 4.14 simply running a rpi-update without BRANCH=next? 1. No, it's not stable enough. I'm still running eight of my eighteen Raspberries on 4.14. 2. If you have to ask that you shouldn't be running rpi-update, you ...

The mac address is not secure. You can easily spoof it. There's also only 24-bits of uniqueness. First 24-bits are fixed. We've seen address wrap-around as there are already more than 16million pis out there in the wild and with a random assignment wrap-around occurred before the 16million were sold...